A) Field of the Invention
The present invention relates to a ZnO-containing semiconductor layer and a device using the ZnO-containing semiconductor layer.
B) Description of the Related Art
Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of 3.37 eV at room temperature, and has a relatively large excitonic binding energy of 60 meV as compared to other semiconductors. Source material is inexpensive, and influence upon environments and human bodies is small. It is expected to realize a light emitting device utilizing ZnO. Reports on devices having a high emission efficiency are rare until now, and improvement in device characteristics is a present research issue.
In manufacturing a light emitting device such as a light emitting diode (LED), improving the quality of each layer constituting a device results in improvement in the device quality such as an emission efficiency and electrical characteristics. The quality of a layer, particularly an emission layer in which recombination of electrons and holes occurs, greatly influences an emission efficiency. It is therefore important to improve the quality of an emission layer in order to obtain a better light emitting device. Techniques have been proposed for improving crystallinity of an emission layer by mixing Se or Te in the emission layer (refer to, for example, JP-A-2003-69076).
A contact resistance between semiconductor and an electrode is influenced by a carrier concentration in a contact layer on the semiconductor side. As a resistance of the contact layer is lowered, it becomes possible to improve the characteristics of a light emitting device. Techniques have been proposed for lowering an operation voltage of a ZnO-containing LED by forming a high concentration doping region of p-type impurities between a p-type contact layer and an electrode (refer to, for example, JP-A-2004-95634).